The present invention relates generally to improvements in telephone-line disconnects and the like, and more particularly to new and improved automatic current-sensitive telephone-line disconnects. The disconnects of this invention operate to close the telephone lines when the telephone handset is lifted and the telephone cradle switch is closed; and in the multiline telephone disconnect when a line selection switch is also closed. The disconnects continue to operate when the telephone is being used so as to maintain the telephone line connections between the incoming lines and the telephone network. The disconnect also automatically operates to break all telephone connections between the incoming lines and the telephone when the handset is cradled and the line current drops to zero, so as to prevent the use of the cradled telephone for clandestine listening techniques.
In the field of telephone-line disconnects it has been the general practice to employ manual-type disconnects, such as a plug and jack, to break all telephone connections. Although such devices have served the purpose they have not proved entirely satisfactory under all conditions of service for the reasons that they rely on the user and require him to manually connect the lines prior to each telephone call and then disconnect all lines after each call is completed. This necessity for manual disconnection of the telephone lines is particularly bothersome and time consuming when the telephone includes a plurality of lines for auxiliary purposes in addition to the voice lines, and where a large number of plugs and jacks are involved.
In addition, the telephone-disconnect system disclosed in application, Ser. No. 532,529, filed Feb. 28, 1966 now U.S. Pat. No. 6,192,128 required that a switch be added either in the telephone instrument or externally in close proximity to the telephone. The operation of this switch would initiate the closing of the disconnect. Another disadvantage of the previous disconnect which is overcome by the disconnect disclosed herein is the fact that in the previous disconnect if a telephone line was placed in a hold condition, another line had to be selected within a short time interval or the disconnect would open all telephone lines entering the telephone instrument. Once the disconnect opened all the incoming lines, the additional telephone key bad to be depressed and then the cradle switch or the push button switch had to be closed again in order to reconnect the incoming lines to the telephone.
The general purpose of this invention is to provide a telephone-line disconnect which embraces all of the advantages of similarly employed devices and which possesses none of the aforedescribed disadvantages. The present invention provides automatic protection against the use of cradled telephones as clandestine listening devices by protecting against such techniques as radio-frequency saturation, audio pickup, and hidden transmitters which use the telephone set as a source of power. Several embodiments of single and multiline disconnects are included in this invention in order to meet various operational requirements such as, for example, variations in available telephone line current in different countries.
Each embodiment of this invention uses the same basic principles of operation and provides the best possible automatic isolation between the cradled telephone and all outside wiring by using circuit-breaking devices, such as relay contacts, to break the connections. when the telephone is not in operation, open relay contacts disconnect the telephone from all incoming lines. Means are provided to automatically operate the relays and close the contacts when the telephone is to be used. Upon completion of a call, the handset is cradled and the line current drops to zero which automatically disconnects all wiring to the telephone, thus precluding the necessity of the user disconnecting the multiplicity of lines after each call. In this way the successful operation of the disconnect is not dependent upon the user and is not subject to compromise by personnel error as are manual disconnects. In addition, the system of this invention provides an additional feature not provided by the disconnect system disclosed in application, Ser. No. 532,529 filed Feb. 28, 1966. When a hold is placed on a line in the invention described herein the disconnect will open, but when a new line is selected a switching transient will again cause the multi-line disconnect to automatically close the telephone lines to the telephone network. The system of this invention is completely automatic and the telephone lines are automatically connected and disconnected from the telephone depending upon whether the cradle switch is closed or open, respectively, and in the case of the multi-line disconnect, depending upon whether the line-selection button is closed or open.
An object of the present invention is the provision of a telephone-line. disconnect system which will automatically protect against the use of cradled telephones as clandestine listening devices.
A further object of the invention is the provision of the above-mentioned disconnect system wherein a switching transient caused by operation of the cradle switch or line-selector switch controls the closing of all the telephone lines to the telephone network.
Another object is to provide a telephone-line disconnect system wherein the telephone line current is used to control the opening and closing of all the telephone lines.
Still another object is to provide a telephone-line a disconnect system which automatically disconnects all telephone lines when the telephone is cradled and is not in use.
Yet another object of the present invention is the provision of the above-mentioned disconnect system which will be capable of operation for a wide range of telephone line currents.
Another object is to provide a telephone-line disconnect system which will provide protection against such listening techniques as radio-frequency saturation, audio pick-up and the use of hidden transmitters which use the cradled telephone as a source of power.
A still further object of this invention is to provide a telephone disconnect system which is not dependent upon the user for its operation and which is not subject to compromise because of personnel error.
With these and other objects in view, as will hereinafter more fully appear, and which will be more particularly pointed out in the appended claims, reference is now made to the following description taken in connection with the accompanying drawings in which: